ABS always engaging

Truck is a 2007 Silverado (Classic) with 5.3V8. 39k miles. Great truck until recently.

Recent issue when stopping the vehicle. About 75% of the time, at speeds between 5-10mph, the pedal pulses just like the ABS is engaging as it would normally do on ice or snow, and increases stopping distance.

I've checked the wheel sensor connectors (one on each frame rail). Both have good, tight connections but I disconnected and cleaned anyway.

Would appreciate any thoughts and most importantly if this is under warranty. Seems like a major safety issue to me since the vehicle takes longer to stop.

thanks,

RPG

Truck is a 2007 Silverado (Classic) with 5.3V8. 39k miles. Great truck until recently.

Recent issue when stopping the vehicle. About 75% of the time, at speeds between 5-10mph, the pedal pulses just like the ABS is engaging as it would normally do on ice or snow, and increases stopping distance.

I've checked the wheel sensor connectors (one on each frame rail). Both have good, tight connections but I disconnected and cleaned anyway.

Would appreciate any thoughts and most importantly if this is under warranty. Seems like a major safety issue to me since the vehicle takes longer to stop.

thanks,

RPG

Clean the speed sensor mounting surface for rust build up.
As per TSB on slow speed abs kicking in.
If that fails to help.

You need to get the ABS code and read out what the speed sensors are doing on a ABS capable scanner.
All speed sensors should read out same mph with no drop outs.
For more help.
Post back code no.

This problem will not always set a code, also, watching individual speeds will not always show a drop out. The scanner may not update fast enough to show speed drop out. If problem persists after sensor clean, you need to find a scanner that will show all abs data, this way you can watch the individual solinoids. By watching which one engages first you will be able to tell which sensor is dropping out. This is the best way I have found to isolate whick sensor is the problem. Good luck!

Truck is a 2007 Silverado (Classic) with 5.3V8. 39k miles. Great truck until recently.

Recent issue when stopping the vehicle. About 75% of the time, at speeds between 5-10mph, the pedal pulses just like the ABS is engaging as it would normally do on ice or snow, and increases stopping distance.

I've checked the wheel sensor connectors (one on each frame rail). Both have good, tight connections but I disconnected and cleaned anyway.

Would appreciate any thoughts and most importantly if this is under warranty. Seems like a major safety issue to me since the vehicle takes longer to stop.

thanks,

RPG

with the ABS acting up at low speeds with no reason this is most often the sensors output voltage is too low at the slow speeds.

what causes this is rust on the hub mounting surface or the hub bearing is bad.

you could have all kinds of ABS issues...your issue however is the ABS activation at slow speeds. you do not need a 2ooo.oo scanner OEM licensed to check the sensors..

with a voltmeter set to ac volts 1 or 2volts range measure the sensor voltage at the connector while you rotate the hub with your hands at a good rate ..the voltage should be over 350 MV AC ...OR .35 VOLTS AC OR HIGHER....

IF YOU FIND THAT ONE SIDE IS LOW REMOVE THE SENSOR..spray with penitrating oil and let it soak ...rotate gently to remove...if the grease in the hub is red your bearing is shot...if the grease is blue try to file down the rusted hub sensor mounting surface then repeat the test on the voltage...

If you find no problems as I discribed here then you have a very weird problem...which could cost alot to repair..this would mean most shops would replace everything ...this would be bad...

thank you everyone for the excellent information. I'll post back results.

btw, no ABS codes on a scan. Just a PO449 error (EVAP SOLENOID). Gee, and everything was going so well with this truck

RPG

do yourself a favor and pull the abs fuse while driving untill you find out whats causing it. The brakes will work with the ABS fuse out, however if you slam them it will skid, easier to deal with than the brake failing due to ABS going off when not bneeded casuing you to hit someone or something, like so many have had happen.

thank you everyone for the excellent information. I'll post back results.

btw, no ABS codes on a scan. Just a PO449 error (EVAP SOLENOID). Gee, and everything was going so well with this truck

RPG

I forgot to mention IF you find NO ABS CODE this adds to the sensors/or hub being the cause of the issue you have ......with my test proceedure you will locate if its the rusty hub or the hub bearing is shot.

"I forgot to mention IF you find NO ABS CODE this adds to the sensors/or hub being the cause of the issue you have ......with my test proceedure you will locate if its the rusty hub or the hub bearing is shot".

I_Cat, thanks very much. I'll dig into it tonight. One question. This is a 2 wheel drive vehicle (1500) so I assume there isn't a hub bearing on the front discs, just the traditional two piece Timken bearings on each wheel. Or is there some additional support/bearing that you're referring to?

I admit I haven't done any brake work on the vehicle yet, due to the low mileage.

RPG

"I forgot to mention IF you find NO ABS CODE this adds to the sensors/or hub being the cause of the issue you have ......with my test proceedure you will locate if its the rusty hub or the hub bearing is shot".

I_Cat, thanks very much. I'll dig into it tonight. One question. This is a 2 wheel drive vehicle (1500) so I assume there isn't a hub bearing on the front discs, just the traditional two piece Timken bearings on each wheel. Or is there some additional support/bearing that you're referring to?

I admit I haven't done any brake work on the vehicle yet, due to the low mileage.

RPG

I haven't worked the 2007 - 2011 models. the sensors are mounted in a hole , which is where the toothed wheel is protected from the weather and debris ...this design works better than the 1994 models that got damaged and caused many brake failures.

the sensor should be similar just you don't have a hub like the 4wd model..I would not expect the front bearing to be bad.. at this mileage I would clean and re grease them while your in that area...

I have always regreased the front wheel bearings on my rear wheel drive vehicles every 50,ooomi. had one failure at 250,ooomi on my 1983.

how do you like the strut design with this vehicle ? are they holding up ?